Method of making lead-containing steels



AU8 2, 1960 M. TENENBAUM ETAL 2,947,622

METHOD oF MAKING LEAD-CONTAINING sTEELs 2 Sheets-Sheet 1 Filed June 23.1958 Aug. 2, 1960 M. TENENBAUM l-:TAL

METHOD oF MAKING LEAD-CONTAINING sTEELs 2 Sheets-Sheet 2 Filed June 23,1958 Zi/zy. 5.

METHO OF MAKING LAD-CONTAINING STEELS Michael Tenenbaum, Flossmoor,lll., and James W. Halley, Chesterton, and Frank W. Luerssen, Munster,Ind., assignors to Inland Steel Company, Chicago, Ill., a corporation ofDelaware Filed June 23, 1958, Ser. No. 743,708

3 Claims. (Cl. 75-129) This invention relates to steel. Moreparticularly,

this invention is concerned with a novel process of promachineabilitycharacteristics compared to unleaded steels. Lead containing steels arecommercially available and are widely used where high speed machining ofexcellent quality is required.

The production of lead containing steels has been effected in a numberof ways. One method tried was to introduce lead blocks-to molten steelin a ladleor ingot mold. This method was not satisfactory because nearlyall of the lead settled to the bottom with only a small insufficientproportion being dispersed throughout the steel. Even when the lead wasadded by pouring in small pieces of lead the result was notsignificantly different. A better method, and one that proved usefulcommercially, wasto introduce the lead in the form of a continuousstream of small pellets directly into ya stream of molten steel flowinginto a mold, such as an ingot mold. Such a method, however, requirescareful coordination of the flow of each stream, considerable manuallabor and supervision and maintenance of the lead delivering equipment.These and other similar prior art methods of addition were all based onthe assumption that lead is completely insoluble in molten steel andthat, therefore, it was necessary to break up and disperse the leadparticles in the molten steel just before freezing so that they wouldbecome entrapped in the steel. In practice, however, globules of leadwere frequently found in ingots produced in this way.

A new, simple and efiicient method of introducing lead into steel hasnow been discovered. According to the present invention this method, inone of the broad aspects thereof, comprises feeding a stream of moltensteel to molten lead, separating the molten steel and molten lead intotwo layers by gravity settling, removing the upper layer comprisingsteel having a small amount of lead dispersed therein and solidifyingthe leaded steel so produced.

The method of this invention yields leaded steel remarkably free of leadglobules and particles. This is due primarily to the gravity settlingwhich permits lead particles to separate from the steel before the steelis solidi- `tied, as by introduction into an ingot mold. However, it isalso apparently the result of a more uniform and thorough distributionof the lead in the steel, perhaps even as a true solution, than wasachieved by prior art methods in which lead concentrations were oftenundesirably localized in certain areas, even though not present asglobules.

The invention will now be described further in conjunction with theattached drawings in which:

Fig. l is a plan view of a vessel forV holding and separating the moltenlead and steel and conveying the leaded steel to a mold.

Fig. 2 is a sectional view of the vessel of Fig. 1 taken at theline 2 2;

Fig. 3 is a plan view of 4another type of vessel which may be used inthe invention to hold the molten lead and effect separation of the,molten steel therefrom; and

Fig. 4 is a sectional view of the vessel of Fig. 3 taken at the line 44.

The vessel shown in Figs. l and 2, generally called a tundish, is madeof a suitable refractory material.V The vessel l10 ordinarily has areinforcing. cover 11.` The vessel is shaped to provide a bowl area 12which' has lip 13 lower than the other sides of the bowl to permitexcess molten material in the bowl to ow over the lip 13, down thedischarge conduit 14 and out the orifice 15. In the practice of thisinvention molten lead 16 is placed in the bowl 12 but to a levelappreciably below the lip 13. A stream of molten steel `18 is thencaused to flow into the bowl and into the molten lead where the steelstream is dispersed. The molten steel, being the lighter of the twometals, rises to form an upper lead-containing steel layer 17 over themolten lead. As the molten steel stream 18 continues to flow, the leadcontaining steel layer 17 continues to rise until it spills over lip 13,iiows through conduit 14 `and out discharge orifice 15. The leaded steelmay then be directed-to an ingot mold.

A modiied tundish adapted for production of larger quantities of leadedVsteel and increased lead settling is shown in Figs. 3 and 4. The vessel30 of refractory ymaterial is reinforced -With a steel cover 35. It hasbowl area 31 which functions as a lead reservoir and steel-lead mixingand settling area. The bowl 31 has-"a dam 32 on one side lower than theother threevsides. The molten steel which ows over the dam 32, goesthrough conduit 33 and flows out nozzle 34.

In practicing the invention using a vessel as shown in Figs. 3 and 4 amolten pool of lead 36 is provided in the bowl 31 but of insufficientvolume to fill it completely; a maximum of one-half to two-thirds isgenerally satisfactory. A stream of steel 38 is then directed into thepool of molten lead with sufficient force or velocity to be dispersedthoroughly in the lead. By this action and through the steel rising tothe surface of the lead, small amounts of lead become uniformly andthoroughly dispersed in the steel. stream 38 causes the lead-bearingmolten steel layer 37 to build up until it flows over the dam 32 and.into conduit 33 from which it may be directed into a mold. If desired astopper may be provided in the conduit to regulate, or stop completely,the iiow of lead-containing molten steel through the conduit.

Obviously, .as leaded steel is produced using vessels such as thoseillustrated by the drawings, the amount of lead in the reservoir will bereduced. The rate of lead consumption can be readily determined,however, and the necessary quantities -added periodically to maintain asuitable lead supply.

The quantity of lead dispersed in a steel using this process can bevaried by changing the velocity of the steel stream, the depth of moltenlead in the reservoir and the total volume of lead present. It isgenerally, however, unnecessary to produce leaded steels containingminimum or maximum amounts of lead. The desired amount of lead, i.e.,0.20 to 0.35%, will normally be dispersed in the steel by following theinvention employing considerably varied conditions and equipment.

The following examples are presented to illustrate the invention.

Example 1 To a tundish as in Figs. 1 and 2, 16 long, 81/2" wide and 6deep there was added 30 lbs. of molten lead at a temperature of 1500 F.to the bowl area. About 300 lbs. of molten steel was poured in a streaminto the molten The continuous addition of steel by lead continuously.The layer of leaded steelV spilled over the lip and was discharged intoan ingot mold. The lead analysis of the ingot was as follows:

Percent ngot height: Lead analysis, percent Example 2 One thousandpounds of lead in the molten state was placed in the bowl of a vessel ortundsh as shown in Figs. 3 and 4. The tundish was 88 long, 42" wide and42" high. The moltenk lead was at 2500" F. A total amount of about14,900 lbs. of molten steel was added in a stream tothe molten lead inabout two minutes. The molten steel layer on top of the molten leadcontinued to build up until it overowed the dam and passed through the`conduit from which it was directed into an ingot mold. The ingotanalyzed as follows:

Various changes and modications of the invention can be made and, to theextent that such variations incor- 4 porate the spirit of thisinvention, they are intended to be included within the scope of theappended claims.

What is claimed is:

l. The method of dispersing small amounts of lead in steel to increasethe machineability of the steel which comprises feeding a stream ofmolten steel to a pool of molten lead, separating the molten steel andmolten lead into two layers by gravity settling, removing the upperlayer comprising steel having a small amount of lead dispersed therein,and solidifying the leaded steel so produced.

2. The method of dispersing small amounts of lead in steel to increasethe machineability of the steel which comprises separately melting steeland lead, adding the molten steel to a pool ofthe molten lead in astream with sufficient velocity so that it is distributed in the lead,separating the molten steel and molten lead into two layers by gravitysettling, removing the upper layer comprising steel having a smallamount of lead dispersed therein, and solidifying the leaded steel soproduced.

3. The method of producing lead containing steel which comprisespartially illing a vessel with molten lead, feeding a stream of moltensteel into the pool of molten lead with suicient velocity so that thesteel stream is dispersed in the molten lead, separating the moltensteel and molten lead in the vessel by gravity into two layers,continuing the introduction of the molten steel stream into the moltenlead during separation of said layers so that the upper layer of moltensteel containing a small amount of lead dispersed therein overflows thevessel, and directing the lead-containing molten steel which so overowsinto a mold.

References Cited in the le of this patent UNITED STATES PATENTS2,854,716 Funk et al. Oct. 7, 1958`

1. THE METHOD OF DISPERSING SMALL AMOUNTS OF LEAD IN STEEL TO INCREASETHE MACHINEABILITY OF THE STEEL WHICH COMPRISES FEEDING A STREAM OFMOLTEN STEEL TO A POOL OF MOLTEN LEAD, SEPARATING THE MOLTEN STEEL ANDMOLTEN LEAD INTO TWO LAYERS BY GRAVITY SETTLING, REMOVING THE UPPERLAYER COMPRISING STEEL HAVING A SMALL AMOUNT OF LEAD DISPERSED THEREIN,AND SOLIDIFYING THE LEADED STEEL SO PRODUCED.